A total or partial hip replacement procedure is sometimes necessary to repair diseased or damaged parts of the hip joint, and in particular, the femoral head or the acetabular cup of the hip joint. During replacement of the femoral head, the diseased or damaged head is removed and the remaining portion of the femur is shaped to receive the stem of an implant which extends into the medullary canal of the bone. A prosthetic, spherical or ball-shaped head is attached to the top of the stem and replicates the anatomy of the removed femoral head, fitting into either the remaining acetabular cup or an artificial replacement therefore.
Shaping of the femoral canal is accomplished using various shaping instruments in the form of femoral rasps or broaches. Generally, such rasps or broaches are designed to match the shape of the stem to be used in the replacement implant so that the femur can be shaped to securely receive the implant. Shaping instruments are inserted into the femoral canal using a handle adapted to affix to the end of the shaping instrument. Many handles have been developed that attach to the proximal portion of shaping instruments for introduction and removal of the shaping instrument from the femur of the patient. However, these handles are designed for use in hip replacement procedures that require either a large incision or a posterior approach in order to gain access to the femur, both of which cause severe trauma to the area surrounding the hip joint increasing the patient's pain and recovery time, and can result in increased risk to the patient.
In an effort to provide a safer, less-traumatic surgical procedure for replacement of the femoral head, it has been determined that an anterior approach to the proximal femur causes less trauma to the surrounding tissue. An anterior approach is already necessary to gain access to the acetabulum for replacement thereof; thus, the ability to take an anterior approach to the femur eliminates the need for a second incision, or a single, large incision. Additionally, an anterior approach requires less muscle dissection compared to a posterior approach. Traditional instrument handles, such as straight or single-plane angled handles, are not conducive to use in hip replacement surgery using an anterior approach because this procedure typically does not allow for straight-line access to the femoral canal, especially when using minimally-invasive surgery (MIS) techniques such as decreased incision size. In particular, problems can arise from the use of traditional handles with respect to alignment of the shaping instrument in the femoral canal, which can cause fracture or misalignment of the femoral implant. Furthermore, problems can arise related to tissue damage from extreme pressure that must be applied to the handle while “fighting” against the tissue for alignment of the shaping instrument within the femoral canal.
Previous attempts at developing an instrument handle for use in minimally invasive surgery have attempted to adapt an instrument handle for use with an incision that does not directly align with the femoral medullary canal. This has resulted in a handle having a “dual offset” design in which the handle incorporates a series of three perpendicular bends to offset the shaping instrument from the proximal section of the handle in both the posterior and lateral directions. This configuration results in a section of the handle that is oriented in the proximal-distal direction, followed by a section that is oriented in the medial-lateral direction, followed next by a section that extends in the anterior-posterior direction, from which the shaping instrument extends in the proximal-distal direction. As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.
This type of handle configuration is capable of reaching the femoral medullary canal through an MIS or anterior approach. However, because the handle has two sections that are orthogonal to the direction of movement of the handle, the handle still interferes with the tissue surrounding the femoral medullary canal, resulting in damage thereto. Furthermore, the severity of the bends used in the handle results in a significant loss of linear impaction force from the proximal end of the handle, where the force is applied, to the instrument, where the force acts. This loss in force is due to the tendency of the perpendicular sections to create torque within the handle in both the lateral and anterior directions. While shaping the femoral medullary canal, it is necessary to minimize torque within the shaping handle because such torque is ultimately applied to the bone, which can cause breakage of the bone or misalignment of the implant. At the very least, the loss of the linear force applied to the handle makes it more difficult to shape the medullary canal for acceptance of the implant because the instrument tends to pitch or yaw within the medullary canal.
Therefore, it is desirous to provide a handle for a shaping instrument that allows for the shaping instrument to be introduced through a small incision, preferably on the anterior side of the patient. The handle should allow for proper alignment of the shaping instrument, and adequate linear force transmission, while minimizing damage to surrounding tissue.
During hip replacement surgery, it is often necessary to detach the shaping instrument from its handle. This allows a trial ball-shaped head to be attached to the proximal section of the shaping instrument in a well-known manner for trial reduction of the hip joint. Several variations of such locking mechanisms have been previously developed, but these locking mechanisms are only designed to work with straight or single-plane handles. Therefore, it is also desirous to provide a locking mechanism to attach a shaping instrument to a compound offset handle such that the handle can be easily detached and the handle can be removed from the incision. It is also desirous that this locking mechanism be controlled from the proximal portion of the handle which is located outside of the incision. This prevents the operator from having to reach into the wound to release the handle from or to reattach the handle to the shaping instrument.
Similar advancements are also desired for insertion of the stem portion of an implant into the prepared femoral canal. Preferably, such a device can be used in connection with a minimally invasive or anterior approach to the femoral canal. It is equally important to have accurate control over placement of the implant and adequate force transmission during impaction of the implant as it is with respect to the use of a shaping instrument.
It is therefore, necessary to provide a handle designed for use with a shaping instrument or a femoral implant that can be used in minimally invasive surgery or in surgeries that use an anterior approach to the femoral canal. It is also important for such a device to allow for accurate placement of the instrument or of the femoral implant and accurate and adequate force transmission from the impaction surface to the instrument or stem.